There is a section here on dual booting using systemd boot. Never used it, but it will hopefully work in your case, or at least point you the right way.https://ostechnix.com/dual-boot-windows-and-pop-os/
What laptop is it? On some, not many, you can remove the dgpu. If you can access the bios, it wouldn’t hurt to see if you can set priority order for the gpu used. What do you mean you can’t get past choosing the installation medium? To me that means the usb, iso, etc you are using. I’m probably misunderstanding you, but do you mean selecting the medium in the bios boot screen? Or have you gotten to the part where grub shows up and you can select install. If it’s the bios bit, have you turned off secure boot? If it’s after selecting install arch in the grub menu, wait a tiny bit for everything to load and try pressing ctrl-alt-F3. Doesn’t have to be F3 you can try all the “F” keys. This will switch to a different tty to try and see if the default one is being weird Though I doubt that will help, but worth a shot. If you can get to grub have you tried to disable the kernel module that loads for the dgpu? You should be able to press “e” to go to the bit you can edit stuff in grub. Check out this and see if it helps https://wiki.archlinux.org/title/Kernel_module#Using_kernel_command_line_2 Best of luck!
You may be out of luck for now. https://github.com/sddm/sddm/issues/1399